The overall objective of this research project is to investigate the repair of non-dimer DNA damage induced by solar UV wavelengths (290-320 nm) that are thought to be important in the induction of skin cancer by sunlight and determine the biological significance of these repair pathways through study of mutant cell lines deficient in the repair of non-dimer DNA damage. The ICR 2A frog cell line will be used in this project primarily because it is highly proficient in enzymatic photoreactivation. In this process the UV-induced pyrimidine dimers are selectively removed through the action of DNA photolyase and photoreactivating light, leaving all other photoproducts intact. Therefore, cells can be exposed to 290-320 nm radiation and the pyrimidine dimers selectively removed. This leaves a nearly pure population of non-dimer photoproducts and it is then possible to specifically investigate the repair and biological significance of these lesions.